1. Field of the Invention
The present invention relates to a method for manufacturing a printed circuit board, and particularly, to a method for manufacturing a printed circuit board capable of easily manufacturing a printed circuit board with a simple process in manufacturing a printed circuit board having a surface exposed to an outside of a product such as a memory card.
2. Description of the Background Art
In general, a printed circuit board is being used for electronic machines or products in various forms. Particularly, in case of a portable memory card having a printed circuit board exposed to an outside of a product, flatness of a surface of the printed circuit board greatly affects quality of a product.
FIG. 1 is a bottom view showing a general memory card, and FIG. 2 is a longitudinal sectional view showing a general memory card.
As shown therein, a general memory card 1 is formed such that a semiconductor element 3 is mounted at a surface of a printed circuit board 2, and a lead 4 of the semiconductor element 3 is electrically connected to a pad portion 16. An upper portion of the semiconductor element 3 is covered with a molding 5, and a cap 5 is coupled to an upper portion of the molding 5.
Since a surface of the printed circuit board 2 of the memory card 1, where the semiconductor element is not mounted, is exposed to an outside of a product, as described above, the flatness of the surface of the printed circuit board 2 greatly affects quality of a product.
Hereinafter, a method for manufacturing a conventional printed circuit board for improving flatness of a surface of a printed circuit board, will now be described.
FIGS. 3A to 3F are views showing a conventional method for manufacturing a printed circuit board.
First, as shown in FIG. 3A, in the conventional method for manufacturing a printed circuit board, inner circuit patterns 11 are formed inside an insulating material in multi-layers, and a plurality of through holes 10a are formed at certain portions of the insulating material 10.
Then, as shown in FIG. 3B, a copper sheet 11a is formed inside the through hole 10a to electrically connect the inner circuit patterns 11 and an outer circuit pattern 13 to be described later.
An outer circuit pattern 13 is formed at an inner circumferential surface of the through hole 10a and the surface of the insulating material 10 so as to be electrically connected to the inner circuit pattern 11. Then, a specific portion of the outer circuit pattern 13 is exposed to light and developed to be removed.
Then, as shown in FIG. 3C, to protect the outer circuit pattern 13, a solder resist layer 14 of general ink or general resin is formed at the entire surface of the insulating material 10 and the entire surface of the outer circuit pattern 13. At this time, solder resist layer 14 is also filled in the through hole 10a, and a sinking portion 14a is formed at a specific portion of the solder resist layer 14 because of a groove 10b (refer to FIG. 3B) generated by the exposure to light and a development.
The sinking portion 14a is generated as the specific portion of the solder resist layer 14 is depressed at the groove 10b in a process of applying solder resist layer 14 to the entire surface of the insulating material 10 and the entire surface of the outer circuit pattern 13.
Then, as shown in FIG. 3D, through an abrading process, the surface of the solder resist layer 14 is flattened.
At this time, the entire surface of the solder resist layer 14 is uniformly abraded until the sinking portion 14a (refer to FIG. 3C) is removed, and a portion 13a (hereinafter, referred to as terminal portion) of the outer circuit pattern 13, which is connected to a semiconductor element (not shown) is exposed.
Then, as shown in FIG. 3E, after the surface is uniformly abraded so that the terminal portion 13a and the solder resist layer 14 are the same in height, a photo solder resist layer 15 is printed at the surface. Then, a specific portion of the photo solder resist layer 15 is exposed to light and developed to thereby expose the terminal portion 13a covered with the photo solder resist layer 15, again.
Then, as shown in FIG. 3F a pad potion 16 is formed by gold-plating the terminal portion 13a, and thus the pad portion 16 is electrically connected to the terminal portion 13a. In this manner, a printed circuit board is completed.
However, the conventional method for manufacturing a printed circuit board has following problems.
In an abrading process for removing a sinking portion of the solder resist layer in order to flatten the surface of the solder resist layer, when the solder resist layer is abraded, the thickness of the terminal portion has to be finely maintained as thick as a planned measurement. However, since the printed circuit board itself is very thin, it is very difficult to perform the abrading operation, maintaining the planned measurement in an actual abrading process.
In the abrading process, if the solder resist layer is abraded too much, the thickness of the terminal portion becomes too thin as shown in FIG. 4A. In contrast, as shown in FIG. 4B, if the solder resist layer is insufficiently abraded, the solder resist layer cannot be fully abraded, and thus the terminal portion cannot be exposed to the outside. Accordingly, performance of the printed circuit board is degraded, and a mal-operation occurs.